Method of making printing blocks



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' of each individual point is determined by the de- Patented Sept. 14, 1937 UNITED STATES METHOD OF MAKING PRINTING BLOCKS Ragnar Wesstriim, Rotebro, and Gillis Vilhelm Henry Olson, Stockholm, Sweden Application March 9, 1934, Serial No. 714,894

. In Sweden March 13, 1933 2 Claims.

In making printing blocks for example for book-or newspaper printing (embossed printing) two different methods are used, according as the original to be reproduced is composed only of complete black and complete white, for instance, a line drawing in Indian ink, or inaddition thereto contains also tones between .black and whitehalf tones-for instance a photographic picture or a wash. To reproduce the original, which is only .black and white, the same is photographed in the usual way. The printing block, made by means of the negative obtained, is called a phototype printing block.

In reproducing an original with half tones, this original is photographed, but with the difierence that a screen is disposed in the camera in front of the plate and at a certain distance from the latter. The screen generally consists of a system of black (non-transparent) lines applied on a transparent material and crossing each other, the distance between two adjacent, parallel lines generally being about equal to the width of the lines. In view of the design such a screen ,is called a square screen, as distinguished from point, line or other screens, which are also used. Each square being transparent but limited by the non-transparent lines, all of the squares will act as small hole objectives, and when the screen is exposed, a point system will be created cover-' ing the whole negative. In such a case the size gree of whiteness of the corresponding point of the picture, on account of which also the half tones will be reproduced. The printing blocks obtained in such a manner are called autotype printing blocks.

If a line drawing, which has been washed in part for instance with a grey tone, so as to indicate shading, or the like, is to be reproduced, the

making of the printing blocks apparently cannot be carried out by direct use of the phototype or autotype method set forth above. In using the former method the half tones would be lost,

whereas the latter method would give a screen tone both in the black and white parts and in the half tone parts of the picture The methods used hitherto for producing such photo-autotype printing blocks are very time wasting, several exposing or copying operations of screen 'tone,

coverings for the etching and the like being required.

' In using screens according to the present invention the said drawbacks are eliminated, the

invention making possible amongst other things.

the direct making of photoautotype printing blocks.

If, for instance, a line drawing is to be reproduced and the same has shades, or half tones, in certain parts which are to be formed of a system of a larger or smaller point shaped printing surfaces, which together correspond to the darker or lighter tones, the shades or half tones of the original may be tinted with a uniform layer of a blue-violet tone colour, the original being then photographed through a screen constructed in the following manner, a square screen being chosen as an example.

According to the above description the square screen consists of non-transparent lines crossing each other, and of transparent squares, limited by the lines. In the screenused in carrying out the method according to the invention, the lines and the squares are made in different transparent colours on a transparent base, for ex-' ample, glass. The different colours, 1. e. the colours of the lines and the colours of the squares, are so chosen that light passing through one of them, is absorbed by the other as completely as possible, i. e. the colours are complementary. If such a screen with blue-violet squares and yellow lines in the above described manner is used in photographing an original, which according tothe abovedescription is made with theshadings in a blue-violet tone of colour, i. e. a tone of colour, which substantially corresponds spectrally with the colour of the screen squares, the said screen will act in the way described below.

The light, which is substantially blue-violet and reflected by the shadings or half tones of the original, passes through the blue-violet squares of the screen relatively unimpaired but is absorbed practically completely by the yellow lines. Thus, the squares are'open and act as uncoloured squares, with respect to the blue-violet light, but the absorbing lines act as if they were black.

In other words only the shades or half tones on the drawing are colored blue, but not the black and white areas. Now, if the screen consisted of yellow lines without blue squares, namely the filters, the blackening on the negative in the parts behind' the squares-would always, in

case of normal times of exposure, be stronger than in the parts behind the lines, as, in fact, the yellow lines absorb about the half of the spectrum, namely the blue-violet part thereof. This would result in an uneven blackening on the parts of the negative which correspond to white parts in the drawing, .which is not desirable, If, however, the squares are madeas blue illters, as

is the case in accordance with the present invention, half the spectrum, viz. the red and green part thereof, will be able to pass through the lines, the remaining half, i. e. the blue and the violet part thereof, passing through the squares. Furthermore, the yellow filter, that is the lines, and the blue filter, that is the squares, as to the concentration of the coloring matters, are so suited relatively to each other that the light reflected from the white parts of the drawing causes as equal a blackening as possible on the negative, i. e. the filter factors of the two filters are equal.

This has the effect that a square with limiting lines, in spite of the fact that both are transparent, will act as a hole objective, which, ac-

, cording to the above description, is the condition of a screen action at this point. Upon the parts of the negative, which correspond to the blue-violet partsof the picture, this screen will thus act as an autotype screen, the screen at these places creating a system of points, in which the size of each point is proportional to the in- 1 tensity, of the penetrating light at the respective part of the picture. The intensity of the light may be altered by variation of the intensity or contents of black of the blue-violet tone of colour (on the original), so that the screen admits of a simultaneous reproduction of half tones of different values. The black parts of the original reflect practically no light, on account of which the difference in absorption between lines and squares is of no eiiect there, and therefore no screen action occurs in these parts of the screen. The latter statement is supported by the fact that the yellow and blue-violet transparent colours, with regard to the necessity of extinguishing thescreen action in the screen parts, which correspond to white picture parts, are so suited relatively to each other (by suitable choosing of the synthesis and concentration ,ofthe colouring matters) that for passing white light reflected from the'white parts of the original, they give the most equal blackening possible on the negative, the emulsion of which is chosen in such a. way that its sensibility is relatively equal to the colours included in the screen.

From the above description it is clear that the new screen, in which the two differently coloured groups of screen elements are complementarily coloured, does not give a screen action inthe parts, which correspond to black and white picture parts but very well in the parts which on' the original have been covered with a tone of colour, which substantially corresponds spectrally with the colour of one group of screen elements (the squares). As distinguished from so-called colour screens which are used in. colour photography (and always in contact with the plate), the

screen here described thus acts as an autotype .screen owing to the formation of-limited small ample. Maintaining the principle, both the design and the combinations of colours of the screen may be varied. In the square screen the screen elements of each group are all of the same shape, but one may, of course, also use screens with one group or the other consisting of screen elements of different shapes, although of the same colour.

In the accompanying drawing one embodiment of the invention is illustrated and Figure 1 shows part of a screen with blue squares surrounded by yellow lines.

Figure 2 illustrates diagrammatically the action of the screen for blue light reflected from blue colored parts of the original; and

Figure 3 illustrates diagrammatically the behavior of the screen to white light reflected from white parts of the original.

'In Fig. 2 the screen point begins to form at the point A on the plate and with A as the center it spreads itself circularly to a maximal radius AB depending upon the existing intensity of light and the length of the time of exposure. The blue light from the lens aperture meeting-the yellow lines is stopped by the same and will never reach the plate. Consequently, it is clear from Figure 2 that the screen acts exactly as an ordinary screen for blue light.

In Fig. 3, relating to white light reflected from white parts of the original, in addition to the formation of screen points for blue light described in connection with Figure 2, which formation is brought about also here for the blue and violet parts of the white light, the yellow lines, in this case, Fig. 3, are penetrated by the yellow and red parts of the white light. Thus, these parts meet the plate and cause blackening between the real screen points, which blackening, if the screen has been made in a correct way, is of an intensity comparable to the blackening of the screen points. As a consequence, the screen action is neutralized for white light.

Having now described our invention, what we claim as new and desire to secure by Letters Pat ent is:

l. A method of making printing blocks comprising, first coloring the half tones of the original with a color, second preparing a screen with two difierently colored series of screen elements, one series being colored with a color which corresponds spectrally with the color of said original, and the other series being .made in another color which is adapted to substantially completely absorb light passing through said first mentioned series of screen elements; thereupon photographing said original through said screen, which thus acts as an autotype screen.

2. A method of making printing blocks comprising, flrst coloring the half tones of the original with a blue-violet color, second preparing a screen with transparent fields of a blue-violet color, providingv yellow border lines for said fields of the screens; thereupon photographing said original through said screen which thus acts as an autotype screen.

RAGNAR wEss'moM. GILLIS vmn. HENRY Orson. 

